1. Field of the Invention
The present invention relates to a dual (or multi) sectional evaporator system of increased refrigeration capacity for use with any air conditioner, refrigeration or heat pump system. This invention more particularly pertains to an apparatus and method comprising a dual (or multi) sectional evaporator system allowing air to first pass through the warmest sections of an evaporator and then to pass through the coldest sections of the evaporator which provides for 2 (or more) exposures of the air stream to the same refrigerant.
2. Description of the Background Art
Presently there exist many types of devices designed to operate in the thermal transfer cycle. The vapor-compression refrigeration cycle is the pattern cycle for the great majority of commercially available refrigeration systems. This thermal transfer cycle is customarily accomplished by a compressor, condenser, throttling device and evaporator connected in serial fluid communication with one another. The system is charged with refrigerant, which circulates through each of the components. More particularly, the refrigerant of the system circulates through each of the components to remove heat from the evaporator and transfer the heat to the condenser. The compressor compresses the refrigerant from a low-pressure superheated vapor state to a high-pressure superheated vapor state thereby increasing the temperature, enthalpy and pressure of the refrigerant. A superheated vapor is a vapor that has been heated above its boiling point temperature. It then leaves the compressor and enters the condenser as a vapor at some elevated pressure where the refrigerant is condensed as a result of heat transfer to cooling water and/or to ambient air. The refrigerant then flows through the condenser condensing the refrigerant at a substantially constant pressure to a saturated-liquid state. The refrigerant then leaves the condenser as a high-pressure liquid. The pressure of the liquid is decreased as it flows through the expansion valve causing the refrigerant to change to a mixed liquid-vapor state. The remaining liquid, now at low pressure, is vaporized in the evaporator as a result of heat transfer from the refrigerated space. This vapor then enters the compressor to complete the cycle. The ideal cycle and hardware schematic for vapor-compression refrigeration is shown in FIG. 1 as cycle 1-2-3-4-1. More particularly, the process representation in FIG. 1 is represented by a pressure-enthalpy diagram, which illustrates the particular thermodynamic characteristics of a typical refrigerant. The P-h plane is particularly useful in showing amounts of energy transfer as heat. Referring to FIG. 1, saturated vapor at low pressure enters the compressor and undergoes a reversible adiabatic compression, 1-2. Adiabatic refers to any change in which there is no gain or loss of heat. Heat is then rejected at constant pressure in process 2-3, and the working fluid is then evaporated at constant pressure, process 4-1, to complete the cycle. However, the actual refrigeration cycle may deviate from the ideal cycle primarily because of pressure drops associated with fluid flow and heat transfer to or from the surroundings.
It is readily apparent that the evaporator plays an important role in removing the heat from the thermal cycle. Evaporators convert a liquid to a vapor by the addition of latent heat. Latent heat is the amount of heat absorbed or evolved by 1 mole, or a unit mass, of a substance during a change of state such as vaporization at constant temperature and pressure. Most commercially available evaporators have a coil of a tubular body extending within the evaporator for the purpose of providing a heat exchange surface. The coil of each evaporator extends in a serpentine manner from the bottom to the top of the evaporator. Often one of the serpentine rows will cross over another of the serpentine rows in an evaporator such that neither of the rows has more of a heat load. In other words, the amount of heat each row has to absorb is equalized by having rows cross over one another so that the entire load is not on one part of the air flow.
However, these known evaporators have drawbacks. The primary drawback results from the fact that no particular attention has been paid to the variations in temperatures that exist between the inlet of refrigerant to the evaporator and the outlet of the refrigerant from the evaporator.
In an evaporator, there exits distinct different regions, which have varying temperatures for many different reasons. One distinct region is the flash gas loss region, which varies in percentage of evaporator surface area because of the temperature of the sub-cooled (liquid temperature below condenser phase change temperature) liquid entering the evaporator's expansion device. This flash gas loss region has a warmer average temperature than the phase change region of the evaporator. The phase change region of the evaporator is the coldest section of the evaporator and is the region where the liquid refrigerant vaporizes to a gas while absorbing heat from the secondary fluid (air) that comes in thermal contact with it. As long as there is any liquid present, the temperature of this region generally stays constant. Another warmer region exists downstream of the phase change region called the superheat region where the saturated vapor absorbs heat as it warms up. This is a region of the evaporator where no more liquid refrigerant exists and the heat absorption capability is strictly based on the temperature change of the saturated vapor. Even in the phase change region there is a temperature gradient caused by the difference in refrigerant pressures between the beginning of the phase change region and the end of the phase change region (due to a pressure gradient caused by frictional line losses). Finally, with the use of azeotropic (2 or more refrigerants blended together that together exhibit a different set of thermodynamic properties from that of the individual refrigerants) mixtures there is a temperature gradient across the phase change region of the evaporator due to "glide" (a difference caused by the difference in phase change temperatures that results from a change in the percentage of each component of the azeotropic mixture across the evaporator's phase change region).
None of the known embodiments of the evaporator art deals with these known temperature differentials that exist within the scope of the entire evaporator surface.
It is known that the most efficient heat exchange between two fluids, occurs when the two fluids flow counter flow to one another, with the warmest region of the first fluid coming into thermal contact with the warmest region of the second fluid and then the first fluid coming into thermal contact with subsequently colder and colder regions of the second fluid, where the purpose is to cool the first fluid to the coldest possible temperature. No known evaporator art has applied this known principle.
Further some of these known evaporators configurations have additional drawbacks. Due to the particular arrangement of the various components within the thermal transfer cycle, the bulk of the evaporator is often presented as a particular burdensome drawback. For example, a 24" by 24" closet would normally only accommodate a 3.5 ton A-coil system with today's commercially available evaporators not including the present invention.
Moreover, known evaporators typically have rectangular shaped cross sections. Therefore, substantial portions of the ends of known evaporators have insufficient air flow. These ends of these known evaporators have wasted air space resulting in lost evaporator surface area.
In response to these realized inadequacies of earlier configurations of evaporators used within the thermal transfer cycle of air conditioners, refrigeration equipment and heat pumps, and their resulting inefficiencies, it became clear that there is a need for dual (or multi) sectional evaporator designs that would take advantage of the known benefits of fluid to fluid counter flow. The results of the use of these new evaporator designs being greater refrigeration capacity and improved dehumidification, both gained at no additional power consumption for the total refrigeration thermal cycle. The greater capacity being realized from the higher mass flow of refrigerant through the evaporator due to improved heat exchange brought about by the application of counter flow principles and greater dehumidification brought about by cooling the air more effectively below the dew point temperature because of the same improved heat exchange. Moreover, there is a need to significantly reduce the dimensions necessary for placement of an evaporator in a cabinet or closet. In as much as the art consists of various types of evaporator and thermal transfer cycle configurations, it can be appreciated that there is a continuing need for and interest in improvements to evaporators and their configurations, and in this respect, the present invention addresses these needs and interests.
Therefore, an object of this invention is to provide an improvement, which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement, which is a significant contribution to the advancement of the evaporator art.
Another object of this invention is to provide a new and improved dual (or multi) sectional evaporator which has all the advantages and none of the disadvantages of the earlier evaporators in a thermal transfer cycle.
Still another objective of the present invention is improved thermodynamic efficiency.
Yet another objective of the present invention is to provide elements of counter flow principles to all possible variations of types and purposes of evaporators, including those with; minimal sub-cooling, maximum sub-cooling, minimal superheat, maximum superheat, low pressure gradients, high pressure gradients, low "glide" temperature spreads, high "glide" temperature spreads, as well as for; flat coils, slant coils or "A" coils, and for; down-flow or up-flow design. The purpose for each design being to put the warmest part(s) of the evaporator upstream in the air flow from the coldest part(s) of the evaporator.
Still a further objective of the present invention is to provide increased refrigeration capacity.
Yet a further objective is to allow for increased latent heat removal and, therefore, increased dehumidification.
An additional objective is to provide an evaporator that is highly reliable in use.
Another objective is to provide an evaporation system having an increased Energy Efficient Ration (EER) as a result of a decrease in wattage input and an increase in refrigeration capacity.
Even yet another objective is to provide dual (or multi) sectional evaporators designed to provide for vaporizing a refrigerant passing through a thermal transfer cycle, where a dual (or multi) sectional evaporator is to be placed in an air stream generated by an air supply and the dual (or multi) sectional evaporator comprising in combination 2 or more sections of the evaporator, positioned in the airstream so that the warmest section(s) of the evaporator is (are) upstream of the coldest section(s) of the evaporator so that the air hitting the upstream section(s) of the evaporator is (are) pre-cooled before hitting the colder down stream section(s) of the evaporator.
Another objective of the present invention is to provide a method for enhancing latent heat removal in a thermal transfer cycle by cooling the air to temperatures even lower than standard evaporators do so that the air is substantially below the dew point temperature of the air. By increasing the temperature difference below the dew point temperature, more humidity is removed and the latent capacity percentage of the total heat removal is increased.
Yet another objective of the present invention is to provide a method for increasing the superheat capacity of a refrigerant in a thermal transfer cycle. This increases the total change in enthalpy of the refrigerant per unit mass flow and thereby increases overall capacity. This is accomplished by putting the warmer superheat region of the evaporator upstream in the air supply from the colder region(s) thereby supplying more heat to this superheat region.
Even yet another objective of the present invention is to provide an apparatus and method that will increase overall refrigerant mass flow thereby increasing refrigeration capacity while doing so in a more efficient manner.
The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a more comprehensive understanding of the invention may be obtained by referring to the summary of the invention, and the detailed description of the preferred embodiment, in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.